Apparatus and method for waterjet cutting

ABSTRACT

Disclosed is an apparatus for water jet cutting including: a water source; a pump communicating with the water source, generating a high pressure water flow; a tank containing an abrasive material in suspension, including a fluid and abrasive particles dispersed homogeneously in the fluid; and a cutting head in fluid communication with the pump and the tank, the cutting head including a mixing chamber. The tank of the abrasive material in suspension is in communication with the cutting head by an abrasive inlet channel and the cutting head is configured to generate a vacuum pressure that draws the abrasive material in suspension through the abrasive inlet channel toward the mixing chamber to mix the abrasive material in suspension and the high pressure water and form a jet of water and abrasive. Also disclosed is a method for generating a water jet cut that can be implemented with the apparatus.

The present invention relates to an apparatus for water jet cutting andin particular to an apparatus in which the water jet comprises water anddispersed abrasive particles. The invention also relates to a method forperforming the water jet cut by means of the aforesaid apparatus.

Water jet cutting is a technology used to cut and/or shape workpiecesmade of various types of materials, making use of a very high pressurejet of water. This type of technology is commonly known as “Waterjet”.

Within this scope, the term “water” should not be understood as limitedto pure water (H₂O) as working fluid. In this context, the term waterrefers to any fluid, if necessary mixed with solid particles, capable offlowing through a tube or an orifice of a nozzle.

Apparatus used for water jet cutting are generally provided with acutting head capable of delivering, through a specific nozzle, a verythin jet of water, with a diameter between 0.1 mm and 0.4 mm, at veryhigh pressure, up to 6,000 bar and more. To cut hard materials, such asmetals, stone, marble, glass, etc., abrasive particles are dispersed inthe water to increase the erosive capacity of the water jet.

These known apparatus are divided mainly into two categories as afunction of the type of technology applied: “Abrasive water jet” (AWJ)apparatus and “Abrasive Suspension Jet” or “Abrasive Slurry Jet” (ASJ)apparatus.

In the former, i.e., AWJ apparatus, the high pressure fluid, typicallywater, and the abrasive, in the form of dry powdery particles, areconveyed separately into a nozzle comprising a mixing chamber where thetwo aforesaid elements are mixed before flowing out.

These apparatus, although effective and reliable, have some limits. Forexample, the presence of air dispersed in the jet delivered from thenozzle means that this type of apparatus cannot be used in someapplications, such as cutting potentially explosive objects or submergedobjects. Moreover, with this technology, a non-negligible part of thekinetic energy accumulated by the water accelerated in the nozzle isdispersed through the chaotic movement of the abrasive particles in thefocusing tube of the nozzle. Moreover, this also causes rapid wear ofthis tube that, generally, must be replaced after a few dozen hours ofuse.

Another disadvantage linked to this type of apparatus consists in theneed to use dry abrasive particles. This means that it is impossible torecover and reuse in the same machining cycle the part of wet abrasiveparticles that, after a first use, are still sufficiently large to beused for further machining operations.

For this reason, at the state of the art, the wet abrasive particles arecollected and sent to recovery centers equipped with systems dedicatedto the filtration, selection and drying of the reusable particles.

On the contrary, in ASJ apparatus the abrasive and a fluid are mixed,obtaining a suspension (called “slurry”). In general, the fluidcomprises water and additives to form a suspension that maintains theabrasive particles suspended in said fluid for a given period of time.With this arrangement, the particles are prevented from precipitatingdownward and accumulating with the risk of blocking the apparatus.

This suspension is then pressurized and conveyed toward the nozzle.

In general, in these apparatus only a part of the total flow of water ofthe apparatus is mixed with the abrasive to form a first flow (slurry).The first flow and the remaining part of water, conveyed in a secondflow, are pressurized and sent toward the nozzle.

In some of these apparatus, the two flows are mixed upstream of thenozzle, while in others they are mixed directly in the mixing chamber ofthe nozzle.

Although apparatus thus configured partly overcome the limits of AWJsystems, they also have some drawbacks. Among these, the most consistentproblem concerns high wear caused by the flow of abrasive in suspensionon the various components of the apparatus and in particular on thevalves and on the pumping means. For this reason, these systems are notwidely used today, above all in the machine tool sector.

In this context, the object of the present invention is to propose anapparatus and a method for water jet cutting that overcome the problemsof the prior art described above.

Therefore, an object of the present invention is to propose an apparatusfor water jet cutting that can be used without limitations in a widerange of applications.

Another object of the present invention is to propose an apparatus, anda related method, that guarantees an improved penetration capacity inhard materials and at the same time an improved finish of the machinedsurface.

Another object of the present invention is to propose an apparatus forwater jet cutting that is simple to produce, therefore inexpensive, andthat requires limited maintenance.

A further object of the present invention is to provide an apparatus anda method for water jet cutting that allow the operating cost of themachining operations to be greatly reduced.

Besides the aforesaid objects, a further object of the present inventionis to produce an apparatus and a method for water jet cutting thatenables the environmental impact of the waste materials to be reduced.

These and other objects are achieved by an apparatus for water jetcutting comprising:

-   -   a water source;    -   pumping means, in communication with the water source, to        generate a high pressure water flow;    -   a tank containing an abrasive material in suspension, wherein        said abrasive material in suspension comprises a fluid and        abrasive particles dispersed homogeneously in the aforesaid        fluid; and    -   a cutting head in fluid communication with said pumping means        and said tank of the abrasive material in suspension, said        cutting head comprising a mixing chamber for mixing the water        and the abrasive material in suspension.

According to the invention, the source of abrasive material insuspension is in communication with said cutting head by means of anabrasive inlet channel. The cutting head is instead configured togenerate a vacuum pressure that draws the abrasive material insuspension through said abrasive inlet channel toward the mixingchamber.

On the contrary to known ASJ systems, the abrasive material insuspension is not pumped at very high pressure toward the nozzle, but isonly transported, preferably at atmospheric pressure, toward the mixingchamber in which it is intercepted by the high speed water jet beforeentering the focusing tube. This suction is caused by the Venturi effectthat is created in the mixing chamber when the flow of pressurized wateris made to pass through a narrow orifice before flowing into theaforesaid mixing chamber.

In this way, the components of the apparatus are subject to much lesswear relative to the wear that characterizes known ASJ systems.

Moreover, due the introduction into the mixing chamber of the abrasiveparticles in a fluid suspension, the energy loss caused by thedisorderly movement of said abrasive particles, when intercepted by thepressurized water jet, is reduced. This makes it possible to increasethe distance for which the jet of water and abrasive delivered from thenozzle remains cohesive, i.e. maintains a substantially constant width.Tests carried out by the applicant show that the apparatus thusconfigured guarantees, with the same water pressure and the same typeand amount of abrasive material, an increased cutting depth and improvedsurface finish (i.e., less roughness) relative to a conventional systemof AWJ type. Moreover, the more orderly flow of the abrasive particlesinside the focusing tube allows a reduction of the wear of thiscomponent relative to an aforesaid AWJ system.

According to an aspect of the invention, the inlet channel of theabrasive material can be equipped with flow regulating means of theabrasive material in suspension.

According to another aspect of the invention, the abrasive material insuspension comprises abrasive particles dispersed in a liquid or,preferably, gelatinous substance. Advantageously, said gelatinoussubstance comprises at least water and a gelling agent.

According to another aspect of the invention, in the abrasive materialin suspension the volume ratio between the abrasive particles and theliquid or gelatinous substance is preferably from 1:3 to 1:7.

According to another aspect of the invention, said cutting headcomprises a focusing tube of the jet (or nozzle) with a diameterpreferably between 0.5 mm and 1.3 mm. The nozzle has a length preferablybetween 100 mm and 200 mm. The nozzle thus structured guarantees agreater cohesion of the water jet and abrasive delivered, up to adistance of around 60 mm, i.e., around five times higher than that of aconventional AWJ system.

According to another aspect of the invention, the flow regulating meansare mounted at an outlet of the abrasive material of the aforesaid tank.Said flow regulating means can comprise, for example, an opening,through which the abrasive material in suspension can flow, and a movingpartition, associated with control means, adapted to obstruct or partlyor totally free the aforesaid opening. This system, particularly simple,allows rapid dosing of the amount of abrasive material present in thewater jet delivered. The regulating system thus produced allows rapidcalibration of the apparatus as a function of the material of the objectto be processed and of its dimensions.

According to another aspect of the invention, the apparatus can comprisea mixing device to mix the water, the gelling agent and the particles ofabrasive material to form the abrasive material in suspension. Saidmixing device is preferably equipped with pumping means to transfer theabrasive material in suspension into the tank.

According to another aspect of the invention, the apparatus can comprisedosing means, associated with said mixing device, to dose the water, thegelling agent and the particles of abrasive material to form theabrasive material in suspension.

The apparatus thus configured is particularly effective to carry outcontinuous or, in any case, lengthy machining operations, as it allowsan abrasive material in suspension with constant properties to be fed tothe source throughout the whole of the machining process.

According to another aspect of the invention, the apparatus can furthercomprise:

-   -   a collection container to collect the water and the abrasive        material, delivered from the cutting head, and the waste        material from processing;    -   a recovery and recycling system of the abrasive material that        includes at least:        -   separation means to separate wet reusable abrasive particles            from non-reusable abrasive particles and waste material; and            optionally        -   transport or pumping means to transfer said wet mass of            reusable abrasive particles into the tank of the abrasive            material in suspension or, more preferably, into the mixing            device.

In this way, the apparatus allows the abrasive material still usable tobe recycled and re-introduced into the machining process. This recyclingstep of the abrasive material allows a significant reduction in theoperating costs of the apparatus, both of those for purchasing theabrasive material and of those for its disposal.

The abrasive material most widely used for water jet cutting is garnet,well known to those skilled in the art. While on the one hand thismaterial guarantees excellent performance, due to its high level ofhardness and resilience, on the other hand it is particularly costly. Infact, it is estimated that, on average, the costs for purchasing garnetabrasive can represent up to 40%-60% of the operating cost of theapparatus.

Given that after a machining operation a large percentage of theabrasive particles discharged is still sufficiently large to be used ina new machining cycle, recycling of the aforesaid particles is withoutdoubt desirable. This percentage varies in general between 30% and 70%,as a function of the hardness and thickness of the material beingprocessed.

Known systems for abrasive recycling are provided with means to separateand eliminate, from the material collected, both particles with a sizebelow a given threshold, which can comprise powdered particles ofabrasive and of the material of the processed workpiece, and particleswith a size above a given threshold, which generally comprise onlymaterial of the processed workpiece.

The particles of the correct size, which are therefore recyclable, aredried and stored to be re-introduced into the machining cycle.

In some systems this drying step precedes the separation step and iscarried out on the whole mass of abrasive material collected from thecollection tank. In other systems, separation of the recyclable abrasiveparticles instead takes place before the drying step.

Examples of these systems are described in WO 9817439 A2 and U.S. Pat.No. 6,328,638 B1.

Recycling systems thus produced are characterized by very high energyconsumption, due mainly to the particle drying step. In fact, thisenergy consumption makes the recycling step particularly costly, to theextent that the cost of the recycled abrasive is substantially the sameas that of the material purchased from the manufacturer.

In the apparatus of the present invention, the mass of recyclableabrasive material can be re-introduced into the apparatus still wet,eliminating the need for the drying step.

According to a preferred aspect of the invention, the recovery andrecycling system is equipped with pumping means to convey said wet massof reusable abrasive particles into the mixing device.

The objects are also achieved with a method for generating a water jetcut with an apparatus for water jet cutting, which comprises thefollowing steps:

-   -   providing a water source;    -   preparing an abrasive material in suspension, this latter        comprising a fluid and abrasive particles dispersed        homogeneously in the aforesaid fluid;    -   pumping the high pressure water into a mixing chamber of a        cutting head;    -   generating a vacuum pressure in the mixing chamber to draw the        abrasive material in suspension into said mixing chamber through        an abrasive inlet channel;    -   mixing, in said mixing chamber, the pressurized water and the        abrasive material in suspension; and    -   discharging a jet of water and abrasive material from a focusing        tube in communication with the mixing chamber.

According to an aspect of the invention, the step of preparing theabrasive material in suspension comprises the stage of mixing the fluidand the abrasive particles to disperse them homogeneously therein. Saidmixing is preferably carried out in a tank comprising agitator means.

According to another aspect of the invention, the step of preparing theabrasive material in suspension comprises a further stage, preceding themixing stage, consisting of dosing the fluid and the abrasive particles.

According to another aspect of the invention said fluid is a gelatinoussubstance. According to this variant, the method comprises the stage ofmixing water, at least one gelling agent and particles of abrasive toform said gelatinous substance.

The method can then comprise a further stage, preceding the mixingstage, consisting of dosing the water, the gelling agent and theabrasive particles.

According to the invention, the abrasive material in suspension preparedis, preferably, pumped into a tank from which it is then conveyed intothe mixing chamber. The fact of dispersing the abrasive particles in agelatinous substance offers the advantage of being able to store theabrasive material in the tank for many hours without the particlesprecipitating downward, i.e., depositing on the bottom of the tank. Theapparatus thus has a stock of material in suspension ready for use thatallows it to be started immediately and at any time.

The step of dosing and subsequent mixing of the water, of the gellingagent and of the abrasive particles, carried out in the mixing device,ensures that said abrasive material in suspension has the exactconcentration of abrasive particles desired, guaranteeing constantquality and repeatability of the cutting operations.

According to another aspect of the invention, the method also comprisesthe following steps:

-   -   collecting at least a part of the jet of water and abrasive        delivered from the cutting head in a collection container;    -   separating wet reusable abrasive particles from non-reusable        abrasive particles and from waste material; and    -   transferring said wet mass of reusable abrasive particles into        the tank of the abrasive material in suspension or, more        preferably, into the mixing device.

According to this last variant, the step of preparing the abrasivematerial in suspension comprises the mixing of water, at least onegelling agent, said wet or dry abrasive particles, or both wet and dryabrasive particles.

Further characteristics and advantages of the present invention willbecome more apparent from the description of an example of a preferred,but not exclusive, embodiment of an apparatus for water jet cuttingillustrated schematically in the accompanying FIG. 1:

With reference to the FIGURE, the reference number 1 indicates as awhole an apparatus for water jet cutting. As mentioned above, within thecontext of the present invention the term water must be interpretedextensively, hence with reference to any liquid and, even moregenerally, fluid, solid or combinations thereof, provided that it issuitable to be treated (compressed, transferred, conveyed) with thenormal devices used for a fluid and in particular suitable to be forcedinside an orifice of small size, such as the focusing nozzle of theapparatus.

The apparatus is then supplied with a water source 2 to supply theaforesaid process water to the apparatus. The water source 2 cancomprise a tank or a continuous feed line. The source 2 can be equippedwith water treatment devices to treat the process water to make it moresuitable for use in high pressure pumping apparatus. These treatmentdevices are well known to those skilled in the art and shall not bedescribed in more detail. A water line 3 connects the water source 2 topumping means 4.

Said pumping means 4 can comprise a common waterjet pump, for example anintensifier pump, a reciprocating pump, a direct-drive pump or aservo-electric pump.

Said pumping means are generally configured to convey the process waterat a pressure typically between 3000 and 6000 bar.

A water infeed line 5 places said pumping means 4 in communication withthe cutting head 10 of the apparatus.

The apparatus 1 further comprises a source, indicated as a whole with20, of an abrasive material in suspension 21. In the variantillustrated, the source of abrasive material in suspension 20(hereinafter also only “abrasive material”), comprises a tank 22 inwhich the abrasive material in suspension 21 can be deposited. Anabrasive inlet channel 23 places the tank 22 in communication with thecutting head 10.

According to the invention, said abrasive material in suspensioncomprises a liquid or, preferably, gelatinous substance in whichparticles of abrasive material are dispersed. Examples of abrasivematerials that can be used in the apparatus of the invention are garnet,glass, metal grits based on aluminum or the like.

A gelatinous substance is particularly advantageous as it allows theabrasive particles to remain suspended, and hence dispersedhomogeneously, for several hours, preventing them from precipitatingthrough gravity and accumulating at the bottom, mainly, of the tank 22.

The abrasive material in suspension can therefore be prepared and storedin a tank of the apparatus ready for use.

Preferably the suspension is formed with a water-based gelatinoussubstance.

More in detail the suspension comprises water and a gelling agent.

The volume ratio between the amount of abrasive material and of theliquid or gelatinous substance is preferably from 1:4 to 1:8 and morepreferably from 1:5 to 1:7.

According to the invention, the cutting head 10 comprises a body 11 inwhich a mixing chamber 12 is provided. The mixing chamber 12 is in fluidcommunication with the water infeed line 5 and with the abrasive inletchannel 23.

The pressurized water is forced into an orifice 13 from which it flows,at a very high speed, into the mixing chamber 12. The high speedgenerates a vacuum pressure in the mixing chamber 12, which in turndraws the abrasive material in suspension 21 from the tank 22 throughthe abrasive inlet channel 23. The abrasive material in suspension 21and the water jet are then mixed in the mixing chamber 12 and,subsequently, conveyed into the focusing tube 14 from which a jet 15 ofwater and abrasive material is delivered.

A suitable cutting head is, for example, the model Dialine manufacturedand marketed by Hyperterm Inc. or the model Slice Two manufactured andmarketed by Diamond Technology Innovations.

Advantageously, according to the invention, this nozzle is equipped witha focusing tube of the jet with a length preferably between 100 mm and200 mm and more preferably between 140 mm and 160 mm. The nozzle thusconfigured creates a jet of water and abrasive material capable ofremaining cohesive for a greater distance relative to that of aconventional AWJ system, allowing a greater depth of this jet with thesame material processed.

According to a preferred variant, said focusing tube comprises twoportions of tube joined together by a removable connection means (notillustrated). In this way, it is possible to use, as portions, focusingtubes of smaller standard length, which are more widely available andless costly. Moreover, as the portion closest to the outlet of the jetis subject to greater wear, said portions can be disassembled andreversed after a given period of operation, thereby advantageouslyextending the life of the focusing tube before replacement.

Suitable focusing tubes are, for example, the models Roctec 100 orRoctec 500, manufactured and marketed by Kennametal Inc.

To regulate the amount of abrasive material in suspension 21 introducedinto the mixing chamber 12, the apparatus is equipped with flowregulating means 27. Said flow regulating means 27 preferably comprise amoving partition positioned on the abrasive inlet channel 23 or,preferably, directly on the abrasive outlet on the tank 22.

The moving partition, by widening or narrowing the section of theopening for the flow of abrasive material to pass through, regulates theflow of this material conveyed toward the mixing chamber as a result ofthe vacuum pressure.

The moving partition can be moved either manually or by means of anelectric or pneumatic actuator associated therewith.

In a preferred variant of the invention, the apparatus is equipped witha mixing device 24 provided with agitator means to mix the abrasiveparticles and the liquid or gelatinous substance to form the abrasivematerial in suspension 21. Advantageously, said mixing device 24 is incommunication with the tank 22.

A pump 25, if provided, can directly feed the abrasive material insuspension into said tank.

According to another mode of embodiment of the invention, the apparatuscomprises dosing means 26 associated with said mixing device 24 to doseat least the water, the gelling agent and, optionally, the particles ofabrasive material to form the abrasive material in suspension.

Preferably, the gelatinous substance is prepared by mixing water and thegelling agent, this latter being between 0.05% and 5% of the volume ofthe water used, and more preferably around 3%.

According to another variant of the invention, the apparatus is equippedwith a recovery and recycling system of the abrasive material, indicatedas a whole with the reference number 30.

According to the invention, this recycling system comprises a recoverydevice 32 configured to receive a wet mass of abrasive particles and ofwaste material from a collection container 31, positioned in an areabelow the nozzle. The process water and the abrasive material of the jet15, as well as the waste material from processing, are collected in thiscontainer 31. A suitable recovery device is, for example, described inU.S. Pat. No. 6,299,510 B1.

According to the invention, the recycling system 30 also comprisesseparation means 33, adapted to separate the wet mass of reusableabrasive particles from the wet mass of non-reusable abrasive particlesand from the waste material.

In particular, these separation means 33 are configured to separateparticles with a size greater than a given value, comprising processingwaste from the workpiece, and particles with a size below a giventhreshold, comprising both processing waste and crushed particles ofabrasive. These products are conveyed into a waste container 36 to bedisposed of correctly.

Typically, the separation means 33 comprise a cyclone device 34, ifnecessary associated with a filter device 35.

These devices are well known to those skilled in the art and thereforewill not be described in more detail.

The wet mass of reusable abrasive particles can then be stored in acollection tank 37 or, preferably, conveyed toward the source of theabrasive material in suspension 20, for example by means of an auger orequivalent pumping means.

Advantageously, this wet mass of reusable abrasive particles can beconveyed directly into the mixing device 24 for the production of otherabrasive material in suspension to be used in the machining process.

According to this variant, further dosing means are preferably providedto control the amount of recycled abrasive material introduced into themixing device 24.

Therefore, also in this case the apparatus guarantees that the abrasivematerial in suspension prepared has the correct percentage of dispersedabrasive particles. Moreover, with this system it is also possible, ifnecessary, to introduce new dry abrasive particles into the mixer and todose their amount relative to the amount of recovered wet particles.

With the recycling system thus configured it is possible to recyclebetween 30% and 70% of the abrasive material used, as a function of thehardness of the material and of the thickness of the machined workpiece.

Due to the re-introduction of the wet mass of reusable abrasiveparticles, the recycling system is particularly advantageous from thepoint of view of operating costs, making recovery and recyclingprofitable also for users of apparatus for water jet cutting.

Said recovery operations of the abrasive material can be implementedcontinuously during operation of the cutting apparatus. If the amount ofabrasive particles recovered is not sufficient to guarantee the correctflow of abrasive material in suspension, new dry particles can be mixedwith the recovered wet particles, the water and the gelling agent.

The invention has been described purely for illustrative andnon-limiting purposes, according to some preferred embodiments. Thoseskilled in the art may find numerous other embodiments and variants, allfalling within the scope of protection of the claims below.

1. Apparatus (1) for water jet cutting comprising: a water source (2);pumping means (4), in communication with the water source, to generate ahigh pressure water flow; a tank (22) containing an abrasive material insuspension (21), wherein said abrasive material in suspension comprisesa fluid and abrasive particles dispersed homogeneously in the aforesaidfluid; and a cutting head (10) in fluid communication with said pumpingmeans (4) and said tank (22), said cutting head comprising a mixingchamber (12); wherein said tank (22) is in communication with saidcutting head (10) by means of an abrasive inlet channel (23) and saidcutting head (10) is configured to generate a vacuum pressure that drawsthe abrasive material in suspension (21) through said abrasive inletchannel (23) toward the mixing chamber (12) to mix the abrasive materialin suspension and the high pressure water and form a jet of water andabrasive substance (15).
 2. Apparatus (1) according to claim 1, whereinthe abrasive inlet channel (23) is equipped with flow regulating means(27) of the abrasive material in suspension (21).
 3. Apparatus (1)according to claim 1, wherein said abrasive material in suspension (21)comprises abrasive particles dispersed in a gelatinous substance. 4.Apparatus (1) according to claim 3, wherein said gelatinous substancecomprises at least water and a gelling agent.
 5. Apparatus (1) accordingto claim 3, wherein the volume ratio between the abrasive particles andthe gelatinous substance is from 1:4 to 1:8.
 6. Apparatus (1), accordingto claim 4, wherein the volume percentage of the gelling agent in thewater is between 0.5% and 5%.
 7. Apparatus (1) according to claim 1,wherein said cutting head (10) comprises a focusing tube (14) of the jetwith a diameter between 0.4 mm and 1.5 mm, and a length between 100 mmand 200 mm.
 8. Apparatus (1) according to claim 1, wherein at saidcutting head (10) comprises a focusing tube (14) that includes at leasttwo portions of tube joined by a removable connection element. 9.Apparatus (1) according to claim 2, wherein said flow regulating means(27) are mounted at an outlet of the abrasive material of said tank(22).
 10. Apparatus (1) according to claim 9, wherein said flowregulating means (27) comprise an opening, through which the abrasivematerial in suspension can flow, and a moving partition, associated withcontrol means, adapted to obstruct or partly or totally free theaforesaid opening.
 11. Apparatus (1) according to claim 3, furthercomprising a mixing device (24) to mix the water, the gelling agent andthe particles of abrasive material to form the abrasive material insuspension (21).
 12. Apparatus (1) according to claim 11, furthercomprising dosing means (26), associated with said mixing device (24),to dose the quantity of water, of gelling agent and of particles ofabrasive material to form the abrasive material in suspension (21). 13.Apparatus (1) according to claim 1, further comprising: a collectioncontainer (31) to collect the water and the abrasive material, deliveredfrom the cutting head (10), and the waste material from processing; arecovery and recycling system (30) that includes at least: separationmeans (33) to separate reusable wet abrasive particles from non-reusablewet abrasive particles and from waste material; and transport means totransfer said wet mass of reusable abrasive particles into the tank (22)of the abrasive material in suspension or into the mixing device (24).14. Method for generating a water jet cut with a cutting apparatus,comprising the following steps: providing a water source (2); preparingan abrasive material in suspension (21), this latter comprising a fluidand abrasive particles dispersed homogeneously in the aforesaid fluid;pumping the water at high pressure into a mixing chamber (12) of acutting head (10); generating a vacuum pressure in the mixing chamber(12) to draw the abrasive material in suspension (21) into said mixingchamber (12) through an abrasive inlet channel (23); mixing, in saidmixing chamber (12), the pressurized water and the abrasive material insuspension (21); and discharging a jet of water and abrasive material(15) from a focusing tube (14) in communication with the mixing chamber(12).
 15. Method according to claim 14, wherein the step of preparingthe abrasive material in suspension (21) comprises the stage of mixingthe fluid and the abrasive particles.
 16. Method according to claim 14,wherein the fluid is a gelatinous substance.
 17. Method according toclaim 16, wherein the step of preparing the abrasive material insuspension (21) comprises the stage of mixing water, at least onegelling agent and particles of abrasive to form said gelatinoussubstance in which the particles of abrasive are suspended and dispersedhomogeneously.
 18. Method according to claim 15, wherein the step ofpreparing the abrasive material in suspension (21) comprises a furtherstage, preceding the mixing stage, consisting of dosing the fluid andthe abrasive particles.
 19. Method according to claim 17, wherein thestep of preparing the abrasive material in suspension (21) comprises afurther stage, preceding the mixing stage, consisting of dosing thewater, the gelling agent and the abrasive particles.
 20. Methodaccording to claim 15, wherein the mixing step is carried out in amixing device (24), said abrasive material in suspension (21) preparedbeing subsequently conveyed into a tank (22) in fluid communication withthe mixing chamber (12).
 21. Method according to claim 14, comprisingthe following steps: collecting at least a part of the jet of water andabrasive delivered from the cutting head (10) in a collection container(31); separating reusable wet abrasive particles from non-reusable wetabrasive particles and from waste material; transferring said wet massof reusable abrasive particles into a tank (22) of the abrasive materialin suspension or into a mixing device.
 22. Method according to claim 21,wherein the step of preparing the abrasive material in suspensioncomprises the mixing of water, at least one gelling agent, said abrasiveparticles, wet or dry, or of both types.